The present invention relates to structures for processing electromagnetic radiation and in particular to a structure that greatly increases the absorption cross-section of small electromagnetic resonators.
Concentrating the light received by an optical device or other device for processing electromagnetic radiation can be important in increasing the effectiveness of the device. For example, the electrical signal obtainable from a radiation detector such as an antenna or photodetector can be increased by increasing the concentration of light received by the detector. Similarly, the ability to detect a radiation taggant, for example, a nanoresonator, is improved by increasing the concentration of light onto the taggant effectively increasing the area over which radiation is absorbed.
Conventional concentrators used for optical systems, such as lenses, are limited in effectiveness for extremely small optical devices such as nanoresonators. For example, the “absorption cross-section” σ0 of a nanoresonator with an isotropic angular response having a resonant wavelength of λ0 is:σ0=λ02/4π  (1)
As a result, generally as the size of the nanoresonator decreases, so does the size of its resonant wavelength and accordingly its absorption cross-section, greatly limiting the energy that can be coupled into the nanoresonator.
Some techniques have been developed to increase the size of the absorption cross-section of the nanoresonator but generally these increases have been less than 10σ0.